The present invention is generally related to the injection molding of plastic parts and is more particularly directed to an internal core lifter for molding and ejecting plastic parts having an undercut and a mold incorporating the core lifter.
Core lifters are typically employed in plastic injection molds to aid in the formation of plastic parts having an undercut which could not normally be formed without employing a mold element that moves out of engagement with the plastic part when the mold is moved from a closed to an open position where the part is ejected. Most internal core lifters consist of a core blade inclined at a predetermined angle and having one end permanently mounted to, or integral with a coupling. Usually, the coupling is mounted to one half of the mold and can slide relative thereto. In known core lifters, the coupling and therefore the core blade is mounted to a support for sliding movement relative thereto when the mold is moved between the open and closed positions.
Historically, the core blade of a core lifter includes a first end that is incorporated into a mold cavity to mold and eject the plastic part. In order for the core blade to assist in the ejection of a plastic part without damaging the undercut therein, the core blade which is oriented at a specific molding angle, and the coupling are compelled to move along the support as the mold opens, to maintain the molding angle. As the core lifter moves, the first end moves away from the undercut, thereby allowing the plastic part to be ejected.
A difficulty associated with prior art core lifters is that each lifter was custom made for use with a particular mold, requiring an injection molding facility to maintain a large inventory of core lifters. In addition, since each core lifter was individually and custom manufactured, they tended to be expensive. Accordingly, there is a present need for an internal core lifter, wherein one lifter finds utility in a plurality of different injection molds.
Based on the foregoing, it is the general object of the present invention to provide an internal core lifter that overcomes the problems and drawbacks of prior art core lifters.
It is a more specific object of the present invention to provide an internal core lifter which with little modification, can be employed in a plurality of different injection molds.
The present invention resides in an internal core lifter for molding and ejecting plastic parts. The internal core lifter includes a core blade defining a longitudinal axis and having a first end section and an opposing second end section, the first end section being configured to cooperate with a mold used to produce the plastic parts. Means for forming an undercut in the molded plastic part are also part of the first end section. In the preferred embodiment of the present invention, a mounting member is coupled to the second end section at least a portion of which projects outwardly from the core blade. A bracket fixedly mountable to a mold ejector plate includes means for slidably and pivotally receiving the mounting member thereby coupling the core blade to the bracket. The ejector plate is movable between a raised and a lowered position. Accordingly, upon completion of a molding operation, the mold is moved from the closed to the open position, and the ejector plate is moved from the lowered to the raised position. This motion of the ejector plate causes the core blade to move upward and away from the undercut, thereby ejecting the part.
Preferably, the means for forming an undercut in the molded plastic part includes a slot extending at least partway through the first end section of the core blade, approximately perpendicular to the core blade""s longitudinal axis. During an injection molding operation, the slot is filled with plastic, which upon solidification forms the undercut in the plastic part. While a slot perpendicular to the core blade axis has been described, the present invention is not limited in this regard as other configurations such as inclined surfaces, or slots oriented at different angles can be employed without departing from the broader aspects of the present invention.
In the preferred embodiment of the present invention, the mounting member is in the form of a pin that extends transversely through the second end section of the core blade. Portions of the pin project outwardly from opposing sides of the core blade approximately perpendicular to the blade""s longitudinal axis. In this embodiment of the present invention, the bracket has a first slot that extends from an upper surface of the bracket partway therethrough and is defined by a pair of opposed sidewalls. The bracket also includes a second and third slot, each in communication with the first slot and extending from a respective one of the pair of sidewalls approximately perpendicular to the first slot. When the internal core lifter is assembled in a mold, the above-described portions of the pin that project outwardly from the core blade are slidably and pivotally received within the second and third slots while a heel defined by the second end section of the core blade resides in the first slot.
A pair of support guides is also provided in this embodiment of the present invention, each defining an edge adapted to engage an outer surface of the core blade. When the internal core lifter is assembled in an injection mold, the core blade extends through an aperture defined by a part of the injection mold referred to by those skilled in the pertinent art to which the invention pertains as a xe2x80x9ccavity blockxe2x80x9d. Each support guide is coupled to the cavity block with the edges of the support guides extending into the aperture and engaging the core blade extending therethrough. Accordingly when the mold is moved from a closed to an open position, the ejector plate to which the above-described bracket is mounted can be moved from the lowered to the raised position so that the core blade slides relative to, and pivots about the edges of the support guides.
The present invention also resides in the mold for producing plastic parts that includes first and second mold halves adapted to move between an open and a closed position. Each mold half defines surfaces that cooperate with surfaces in the other mold half to form a shaped mold cavity. The mold includes an internal core lifter as described above with the core blade extending at least partway through each of said first and second mold halves. The bracket is mounted on an ejector plate forming part of one of the first and second mold halves and slidably and pivotally receives the mounting member coupled to the core blade. The ejector plate is movable between a lowered and raised position. Accordingly, when the first and second mold halves are moved between the closed and open positions, the ejector plate is moved from the lowered to the raised position, causing the mounting member, and thereby the core blade, to slide and pivot relative to the bracket.
Preferably, the ejector defines a recess having a shape complementary to a shape defined by the periphery of the bracket. When the mold is assembled, the bracket is positioned and secured within the recess, preventing any movement of the bracket relative to the ejector plate.